1. Field of the Invention
The present invention relates to a semiconductor device such as a field effect transistor used as, for example, a high-frequency power amplifying device and manufacturing method thereof.
2. Description of the Related Art
In recent years, with advance in power of a high-frequency semiconductor element, high frequency characteristics and reliability in a field effect transistor (to be referred to as a Field Effect Transistor: abbreviated as an FET hereinafter) are required to be improved.
In particular, a nitride-based group-III-V compound semiconductor (to be referred to as GaN-based semiconductor hereinafter) which contains GaN as a principal constituent attracts attention with having a high saturation electron velocity and a high breakdown voltage. In order to apply excellent characteristics held by the GaN-based semiconductor to a device, a reduction in parasitic impedance, especially, source inductance in mounting is important.
In general, in a conventional semiconductor device such as a GaAs-based semiconductor device, by a method of connecting a source electrode to a ground electrode through a via hole, a reduction in source inductance is achieved. For example, as described in paragraph [0026] in Japanese Patent Application Laid-Open No. 2003-258002, a GaAs semiconductor layer is formed on a GaAs substrate, and a source electrode, a gate electrode, and a drain electrode are formed on a surface of the GaAs semiconductor layer. Via holes reaching the source electrode are formed in the GaAs substrate and the GaAs semiconductor layer by continuous etching. The source electrode is connected to a ground electrode formed on a rear surface of the GaAs substrate through the via hole.
In order to apply the method of reducing source inductance by forming a via hole to a GaN-based semiconductor, a SiC substrate used as a substrate of the GaN-based semiconductor layer must be etched. RIE (Reactive Ion Etching) method using a fluorine-based gas is used for the SiC substrate. However, a selectivity of the SiC substrate to the GaN-based semiconductor is large. Therefore, it is disadvantageously difficult to process the SiC substrate in the same manner as that in use of a GaAs substrate.